1. Field of the Invention
The present invention relates to an LCD backlight inverter, and more particularly, to a single stage converter in an LCD backlight inverter, which is embodied into an integrated circuit and has an individual circuit structure for converting DC current into AC current.
2. Description of the Related Art
In general, inverters are inverse transforming apparatuses for converting DC current into AC current. The inverters are widely used in various types, examples thereof include those having a DC motor associated with an AC generator; those using a vibrator, those using a discharge tube, and currently those using a transistor or thyristor.
The above inverters are generally used as a portable AC power source, a fluorescent lamp power source of a vehicle, an emergency power source, a backlight power source for an LCD or other display devices and the like.
It will be described about a structure of the above LCD backlight inverter in reference to FIG. 1.
FIG. 1 illustrates a structure of important parts of a general LCD backlight inverter, in which a DC/AC converter 10 performs transformation in a circuit, and a buck switch (not shown) is connected between a power supply VCC and the DC/AC converter 10 to determine power supply.
The buck switch is on/off controlled in response to an output signal of a driving block 20, which controls the operation of the DC/AC converter 10 so as to convert a DC power into an AC power as shown in FIG. 1.
The power converted into the AC high voltage according to the operation of the DC/AC converter 10 is applied to a downstream lamp so that the downstream lamp lights up. The power via the lamp functioning as a feedback signal F/B is inputted into an inversion (xe2x88x92) terminal of an error amplifier ERR1 constituting a detection signal judging block 40.
The error amplifier ERR1 compares the feedback signal F/B inputted into the inversion (xe2x88x92) terminal with a reference voltage inputted into a non-inversion (+) terminal so as to transmit a compared result into the driving block 20.
Describing the operation of the above structure according to an important function, opening the lamp downstream of the DC/AC converter 10 converts the feedback signal F/B into a low state so that the inverter operates to elevate the voltage in an output terminal a of the error amplifier ERR1.
Since elevating the voltage in the output terminal a of the error amplifier ERR1 generates an overvoltage in the second side of the DC/AC converter, it is necessary to control the inverter so as not to generate a voltage at a predetermined level or more.
Therefore, the elevated voltage in the output terminal a of the error amplifier ERR1 is divided via the first resistance R1 and the second resistance R2, and then transferred into an inversion terminal OLP of a comparator Comp1. The comparator Comp1 compares the input voltage with a reference voltage Va applied to a non-inversion terminal thereof to output a compared value so as to control the overvoltage in the second side by controlling the duty of the driving block 20, i.e. the voltage of the output terminal a of the error amplifier ERR1 which is commonly bound to the output terminal of the comparator Comp1.
The LCD backlight inverter operating as above is designated as a so-called single stage type, which has currently become popular compared to a conventional 2-stage type.
Therefore, at the current tendency that the inverters are rapidly adopting the single stage type, the necessity is increasingly growing for realizing an individual circuit while more elevating the efficiency thereof.
Accordingly the present invention has been made to solve the above problems of the prior art and it is an object of the invention to provide an LCD backlight inverter, and more particularly, to a single stage converter in an LCD backlight inverter which is embodied into an integrated circuit and has an individual circuit structure for converting DC current into AC current.
According to an aspect of the invention to obtain the above object, it is provided a single stage converter in an LCD backlight inverter which includes powering passage alternating means connected between a supply voltage input terminal and a transformer for alternating a power supply passage into the first side of the transformer to allow transformation in the transformer and a plurality of lamps connected to an output terminal of the transformer, the single stage converter comprising: transformer controlling means for receiving a feedback current from the output terminal of the transformer and flowing through the lamps in the size of a stable voltage, comparing the feedback current with a dimming signal and comparing a compared value thereof with a periodically generated triangle wave to control the operation of the powering passage alternating means so as to control the operation of the transformer; shut-down judging means for receiving the feedback current from the output terminal of the transformer and flowing through the lamps in the size of a stable voltage and comparing the feedback current with a reference voltage to compare the size of the current flowing through the lamps so as to judge whether a shut-down takes place; and stabilizing means for receiving a supply voltage inputted through the supply voltage input terminal and comparing the supply voltage with the reference voltage to judge whether the supply voltage is in an overvoltage state so as to recognize the supply voltage as in the overvoltage state, and if it is judged that the shut-down generation judging means judges that the shut-down occurs, providing a judgment signal into the transformer controlling means to adaptively correspond to the shut-down or the overvoltage state.
The single stage converter in an LCD backlight inverter according to the invention is characterized in that the shut-down judging means and the stabilizing means are connected in series, and generally in parallel between the supply voltage input terminal and a feedback current input terminal.
The single stage converter in an LCD backlight inverter according to the invention is characterized in that the shut-down judging means comprises: a first comparator for receiving the feedback current from the output terminal of the transformer and flowing through the lamps in the size of stable voltage into an inversion input terminal thereof and receiving the reference voltage into a non-inversion input terminal to provide a compared value into the stabilizing means; a first transistor for dividing a voltage according to the feedback current and performing on/off operations according to the divided voltage; a second comparator for comparing the voltage applied to the non-inversion input terminal and the voltage applied to the inversion input terminal, the voltage applied to the non-inversion input terminal fluctuating according to the on/off operations of the first transistor; and a latch for outputting or non-outputting an initial bias voltage, which is applied to the input terminal synchronized to fluctuation of the compared value from the second comparator, via the output terminal to maintain or smoothen the periodical triangle wave.
The single stage converter in an LCD backlight inverter according to the invention is characterized in that the stabilizing means comprises: a third comparator for dividing the reference voltage via a plurality of resistances, receiving the divided voltage into a non-inversion terminal, and receiving the supply voltage inputted via the supply voltage input terminal into a non-inversion terminal to compare the divided voltage with the supply voltage and output a signal of compared value via an output terminal, wherein the output signal returns to the inversion terminal; and voltage transforming means for transforming the output signal from the shut-down judging means into a stable voltage and inputting the stable voltage into the non-inversion terminal of the third comparator.
The single stage converter in an LCD backlight inverter according to the invention is characterized in that the voltage transforming means comprises: a second transistor for receiving an output signal from the shut-down judging means into a base terminal; a third transistor having a collector terminal commonly bound to the second and third transistors and a base terminal having a common potential with the collector terminal; a fourth transistor having the base terminal commonly bound to the third transistor and an emitter terminal connected to a ground terminal; a fifth transistor having a collector terminal connected to the collector terminal of the fourth transistor, an emitter terminal applied with the supply voltage and a base terminal having a common potential with the collector terminal; a sixth transistor having the base terminal commonly bound to the fifth transistor and a common emitter terminal applied with the supply voltage; a seventh transistor having a collector terminal applied with the supply voltage, a base terminal connected to the collector terminal of the sixth transistor via a resistance and an emitter terminal connected to the non-inversion terminal of the third comparator; and a Zener diode having a cathode diode connected to the base terminal of the seventh transistor and an anode terminal connected to the ground terminal.
According to another aspect of the invention to obtain the above object, it is provided a single stage converter in an LCD backlight inverter which includes powering passage alternating means connected between a supply voltage input terminal and a transformer for alternating a power supply passage into the first side of the transformer to allow transformation in the transformer and a plurality of lamps connected to an output terminal of the transformer, the single stage converter comprising: transformer controlling means for receiving a feedback current from the output terminal of the transformer and flowing through the lamps in the size of a stable voltage, comparing the feedback current with a dimming signal and comparing a compared value thereof with a periodically generated triangle wave to control the operation of the powering passage alternating means so as to control the operation of the transformer; shut-down judging means for receiving the feedback current from the output terminal of the transformer and flowing through the lamps in the size of a stable voltage and comparing the feedback current with a reference voltage to compare the size of the current flowing through the lamps so as to judge whether a shut-down takes place; and stabilizing means for receiving a supply voltage inputted through the supply voltage input terminal and comparing the supply voltage with the reference voltage to judge whether the supply voltage is in an overvoltage state so as to recognize the supply voltage as in the overvoltage state, and if it is judged that the shut-down generation judging means judges that the shut-down occurs, providing a judgment signal into the transformer controlling means to adaptively correspond to the shut-down or the overvoltage state, wherein the transformer controlling means, the shut-down judging means and the stabilizing means are embodied in one chip.